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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 6130

Mobile Ad hoc Networking (MANET)                              T. Clausen
Internet-Draft                          LIX, Ecole Polytechnique, France
Intended status: Standards Track                             C. Dearlove
Expires: December 31, 2007               BAE Systems Advanced Technology
                                                                  Centre
                                                                 J. Dean
                                               Naval Research Laboratory
                                                  The OLSRv2 Design Team
                                                     MANET Working Group
                                                           June 29, 2007


              MANET Neighborhood Discovery Protocol (NHDP)
                        draft-ietf-manet-nhdp-04

Status of this Memo

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   This Internet-Draft will expire on December 31, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).








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Abstract

   This document describes a 1-hop and symmetric 2-hop neighborhood
   discovery protocol (NHDP) for mobile ad hoc networks (MANETs).


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Applicability Statement  . . . . . . . . . . . . . . . . . . .  7
   4.  Protocol Overview and Functioning  . . . . . . . . . . . . . .  8
     4.1.  Nodes and Interfaces . . . . . . . . . . . . . . . . . . .  8
     4.2.  Information Base Overview  . . . . . . . . . . . . . . . .  9
     4.3.  Signaling Overview . . . . . . . . . . . . . . . . . . . . 10
       4.3.1.  HELLO Message Generation . . . . . . . . . . . . . . . 10
       4.3.2.  HELLO Message Content  . . . . . . . . . . . . . . . . 11
   5.  Protocol Parameters and Constants  . . . . . . . . . . . . . . 12
     5.1.  Interface Parameters . . . . . . . . . . . . . . . . . . . 12
       5.1.1.  Message Intervals  . . . . . . . . . . . . . . . . . . 12
       5.1.2.  Information Validity Times . . . . . . . . . . . . . . 13
       5.1.3.  Link Quality . . . . . . . . . . . . . . . . . . . . . 14
       5.1.4.  Jitter . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.2.  Node Parameters  . . . . . . . . . . . . . . . . . . . . . 15
       5.2.1.  Information Validity Time  . . . . . . . . . . . . . . 15
     5.3.  Parameter Change Constraints . . . . . . . . . . . . . . . 15
     5.4.  Constants  . . . . . . . . . . . . . . . . . . . . . . . . 16
   6.  Local Information Base . . . . . . . . . . . . . . . . . . . . 17
     6.1.  Local Interface Set  . . . . . . . . . . . . . . . . . . . 17
   7.  Interface Information Base . . . . . . . . . . . . . . . . . . 18
     7.1.  Link Set . . . . . . . . . . . . . . . . . . . . . . . . . 18
     7.2.  2-Hop  Set . . . . . . . . . . . . . . . . . . . . . . . . 19
   8.  Node Information Base  . . . . . . . . . . . . . . . . . . . . 20
     8.1.  Neighbor Set . . . . . . . . . . . . . . . . . . . . . . . 20
     8.2.  Lost Neighbor Set  . . . . . . . . . . . . . . . . . . . . 20
   9.  Local Information Base Changes . . . . . . . . . . . . . . . . 21
     9.1.  Adding an Interface  . . . . . . . . . . . . . . . . . . . 21
     9.2.  Removing an Interface  . . . . . . . . . . . . . . . . . . 21
     9.3.  Adding an Address to an Interface  . . . . . . . . . . . . 22
     9.4.  Removing an Address from an Interface  . . . . . . . . . . 22
   10. Packets and Messages . . . . . . . . . . . . . . . . . . . . . 23
     10.1. HELLO Messages . . . . . . . . . . . . . . . . . . . . . . 23
       10.1.1. Local Interface Block  . . . . . . . . . . . . . . . . 24
       10.1.2. Neighbor Address Blocks  . . . . . . . . . . . . . . . 24
   11. HELLO Message Generation . . . . . . . . . . . . . . . . . . . 26
     11.1. HELLO Message Specification  . . . . . . . . . . . . . . . 26
     11.2. HELLO Message Transmission . . . . . . . . . . . . . . . . 27
       11.2.1. HELLO Message Jitter . . . . . . . . . . . . . . . . . 27



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   12. HELLO Message Processing . . . . . . . . . . . . . . . . . . . 29
     12.1. Updating the Neighbor Set  . . . . . . . . . . . . . . . . 29
     12.2. Updating the Lost Neighbor Set . . . . . . . . . . . . . . 31
     12.3. Updating the Link Set  . . . . . . . . . . . . . . . . . . 31
     12.4. Updating the 2-Hop Set . . . . . . . . . . . . . . . . . . 32
   13. Other Information Base Changes . . . . . . . . . . . . . . . . 34
     13.1. Link Tuple Not Symmetric . . . . . . . . . . . . . . . . . 34
     13.2. Link Tuple Symmetric . . . . . . . . . . . . . . . . . . . 35
     13.3. Link Tuple Heard Timeout . . . . . . . . . . . . . . . . . 36
   14. Link Quality . . . . . . . . . . . . . . . . . . . . . . . . . 37
     14.1. Deployment Without Link Quality  . . . . . . . . . . . . . 37
     14.2. Basic Principles of Link Quality . . . . . . . . . . . . . 37
     14.3. When Link Quality Changes  . . . . . . . . . . . . . . . . 38
     14.4. Updating Link Quality  . . . . . . . . . . . . . . . . . . 39
   15. Proposed Values for Parameters and Constants . . . . . . . . . 40
     15.1. Message Interval Interface Parameters  . . . . . . . . . . 40
     15.2. Information Validity Time Interface Parameters . . . . . . 40
     15.3. Information Validity Time Node Parameters  . . . . . . . . 40
     15.4. Link Quality Interface Parameters  . . . . . . . . . . . . 40
     15.5. Jitter Interface Parameters  . . . . . . . . . . . . . . . 40
     15.6. Constants  . . . . . . . . . . . . . . . . . . . . . . . . 40
   16. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 41
     16.1. Message Types  . . . . . . . . . . . . . . . . . . . . . . 41
     16.2. TLV Types  . . . . . . . . . . . . . . . . . . . . . . . . 41
     16.3. LINK_STATUS and OTHER_NEIGHB Values  . . . . . . . . . . . 42
   17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 43
     17.1. Normative References . . . . . . . . . . . . . . . . . . . 43
     17.2. Informative References . . . . . . . . . . . . . . . . . . 43
   Appendix A.   Address Block TLV Combinations . . . . . . . . . . . 44
   Appendix B.   HELLO Message Example  . . . . . . . . . . . . . . . 45
   Appendix C.   Constraints  . . . . . . . . . . . . . . . . . . . . 47
   Appendix D.   Security Considerations  . . . . . . . . . . . . . . 49
   Appendix D.1. Invalid HELLO messages . . . . . . . . . . . . . . . 49
   Appendix E.   Flow and Congestion Control  . . . . . . . . . . . . 51
   Appendix F.   Contributors . . . . . . . . . . . . . . . . . . . . 52
   Appendix G.   Acknowledgements . . . . . . . . . . . . . . . . . . 53
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 54
   Intellectual Property and Copyright Statements . . . . . . . . . . 55













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1.  Introduction

   This document describes a neighborhood discovery protocol (NHDP) for
   a mobile ad hoc network (MANET) [8].  This protocol uses an exchange
   of HELLO messages in order that each node can determine the presence
   and status of its 1-hop and symmetric 2-hop neighbors.  This protocol
   is designed to maintain this information in the presence of a dynamic
   network topology.

   The information maintained by this protocol may be used by other
   protocols, such as MANET routing protocols, for determining local
   connectivity and node configuration.

   This specification describes both the HELLO message exchange, the
   messages being defined as instances of the specification [1], and the
   information storage required for neighborhood discovery.

   This protocol makes no assumptions about the underlying link layer,
   other than support of link local multicast.  Link layer information
   may be used if available and applicable.

   This protocol is based on the neighborhood discovery process
   contained in the Optimized Link State Routing Protocol (OLSR) [7].




























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2.  Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC2119 [5].

   The terms "packet", "message", "address", "address block", "TLV", and
   "TLV block" in this document are to be interpreted as described in
   [1].

   Additionally, this document uses the following terminology:

   Node  - A MANET router which implements this neighborhood discovery
      protocol.

   Interface  - A network device, configured and assigned one or more IP
      addresses.

   MANET interface  - An interface participating in a MANET and using
      this neighborhood discovery protocol.  A node may have several
      MANET interfaces.

   Heard  - A MANET interface of node X is considered heard on a MANET
      interface of a node Y if the latter can receive traffic from the
      former.

   Link  - A pair of MANET interfaces from two different nodes, where at
      least one interface is heard by the other.

   Symmetric link  - A link where both MANET interfaces are heard by the
      other.

   1-hop neighbor  - A node X is a 1-hop neighbor of a node Y if a MANET
      interface of node X is heard by a MANET interface of node Y.

   Symmetric 1-hop neighbor  - A node X is a symmetric 1-hop neighbor of
      a node Y if a symmetric link exists between a MANET interface on
      node X and a MANET interface on node Y.

   Symmetric 2-hop neighbor  - A node X is a symmetric 2-hop neighbor of
      a node Y if node X is a symmetric 1-hop neighbor of a symmetric
      1-hop neighbor of node Y, but is not node Y itself.

   1-hop neighborhood  - The 1-hop neighborhood of a node X is the set
      of the 1-hop neighbors of node X.






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   Symmetric 1-hop neighborhood  - The symmetric 1-hop neighborhood of a
      node X is the set of the symmetric 1-hop neighbors of node X.

   Symmetric 2-hop neighborhood  - The symmetric 2-hop neighborhood of a
      node X is the set of the symmetric 2-hop neighbors of node X.
      (This may include nodes in the 1-hop neighborhood, or even in the
      symmetric 1-hop neighborhood, of node X.)

   Constant  - A constant is a numerical value which MUST be the same
      for all MANET interfaces of all nodes in the MANET, at all times.

   Interface parameter  - An interface parameter is a boolean or
      numerical value, specified separately for each MANET interface of
      each node.  A node MAY change interface parameter values at any
      time, subject to some constraints.

   Node parameter  - A node parameter is a boolean or numerical value,
      specified for each node.  A node MAY change node parameter values
      at any time, subject to some constraints.
































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3.  Applicability Statement

   This neighborhood discovery protocol supports nodes which each have
   one or more interfaces participating in the MANET [8].  It provides
   each node with local topology information up to two hops away.  This
   information is made available to other protocols through Interface
   Information Bases and a Node Information Base, described in Section 7
   and Section 8.

   The protocol is designed to work in networks with a dynamic topology,
   and where messages may be lost, such as due to collisions in wireless
   networks.  If relevant link layer information is available then it
   may be used by this protocol.

   This protocol is designed to work in a completely distributed manner,
   and does not depend on any central entity.  It does not require any
   changes to the format of IP packets, thus any existing IP protocol
   stack can be used as is.  It can use the link local multicast address
   and MANET UDP port specified in [2].

   This protocol uses the packet and message formats specified in [1].
   HELLO messages specified by this protocol may be extended using the
   TLV mechanisms described in [1].  For example, if multipoint relays
   (MPRs) are to be calculated similarly to as in OLSR [7] and signaled
   to neighbors, then this information may be added to HELLO messages
   using an address block TLV.  HELLO messages can also be transmitted
   in packets with messages from other protocols that also use [1].
























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4.  Protocol Overview and Functioning

   This protocol specifies local (one hop) signaling that:

   o  Advertises the presence of a node and its interfaces.

   o  Discovers links from adjacent nodes.

   o  Performs bidirectionality checks on the discovered links.

   o  Advertises discovered links, and whether each is symmetric, to its
      1-hop neighbors, and hence discovers symmetric 2-hop neighbors.

   o  Maintains information bases describing discovered links, their
      MANET interface addresses and status, current and former 1-hop
      neighbors, and symmetric 2-hop neighbors.

4.1.  Nodes and Interfaces

   In order for a node to participate in a MANET, it MUST have at least
   one, possibly more, MANET interfaces.  Each MANET interface:

   o  Is characterized by a set of interface parameters, defining the
      behavior of this interface.  Each MANET interface MAY be
      individually parameterized to accommodate the characteristics
      experienced and the behavior desired on that interface.

   o  Has an Interface Information Base, recording information regarding
      links to this MANET interface and symmetric 2-hop neighbors which
      can be reached through such links.  Each MANET interface has its
      own Interface Information Base.

   o  Generates and processes HELLO messages, according to the interface
      parameters for that interface.

   In addition to a set of MANET interfaces as described above, each
   node has:

   o  A Local Information Base, containing the IP addresses of the
      interfaces of this node.

   o  A Node Information Base, recording information regarding current
      and recently lost symmetric 1-hop neighbors of this node.

   A node may have both MANET interfaces and non-MANET interfaces.
   Interfaces of both of these types are recorded in a node's Local
   Information Base, which is used, but not updated, by the signaling of
   this protocol.



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4.2.  Information Base Overview

   Each node maintains a Local Information Base, which contains:

   o  The Local Interface Set, which consists of Local Interface Tuples,
      each of which records the addresses of an interface of the node.

   Each node maintains, for each of its MANET interfaces, an Interface
   Information Base, which contains:

   o  A Link Set, which consists of Link Tuples, each of which records
      information about a current or recently lost link from a MANET
      interface of a 1-hop neighbor to this MANET interface.  A Link
      Tuple for a lost link is maintained for purposes of advertisement
      in HELLO messages and hence accelerated removal of this link from
      the relevant 1-hop neighbors' Link Sets.  Link quality
      information, if used and available, may be recorded in a Link
      Tuple; if this indicates that a link is of too low quality to be
      currently useable, then that link is also treated as lost.

   o  A 2-Hop Set, which consists of 2-Hop Tuples, each of which records
      a MANET interface of a symmetric 1-hop neighbor, and an address of
      a symmetric 2-hop neighbor of this node.  The former MANET
      interface must have a symmetric link to this interface, and the
      former node must be a symmetric 1-hop neighbor of the latter node.
      The 2-Hop Set is updated by the signaling of this protocol, but is
      not itself reported in that signaling.

   Each node maintains a Node Information Base, which contains:

   o  The Neighbor Set, which consists of Neighbor Tuples, each of which
      records all interface addresses of a 1-hop neighbor.  There MUST
      be a current link from a MANET interface of this 1-hop neighbor to
      a MANET interface of this node, although this link MAY be
      currently considered as lost due to insufficient link quality.
      Neighbor Tuples are maintained in the Neighbor Set as long as
      there are corresponding current Link Tuples in the Link Set. A
      Neighbor Tuple allows all addresses of all interfaces of a 1-hop
      neighbors to be associated with each other, including addresses of
      interfaces not represented in the Link Set. Neighbor Tuples allow
      all addresses of interfaces of symmetric 1-hop neighbors to be
      included in HELLO messages on all MANET interfaces of this node.

   o  The Lost Neighbor Set, which consists of Lost Neighbor Tuples,
      each of which records an address of an interface of a recently
      lost symmetric 1-hop neighbor.  Lost Neighbor Tuples allow
      advertising such addresses as lost, in order that these addresses
      can be removed from other nodes' 2-Hop Sets.



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   These sets are used for describing the protocol in this document.  An
   implementation of this protocol MAY maintain this information in the
   indicated form, or in any other organization which offers access to
   this information.

   This protocol contains a signaling mechanism for maintaining the
   Interface Information Bases and the Node Information Base.  If
   information from the link layer, or any other source, is available
   and appropriate, it may be used to update these.  Such updates are
   subject to the constraints specified in Appendix C.

   Some links in a MANET may be marginal, e.g. due to adverse wireless
   propagation.  In order to avoid using such marginal links, a link
   quality is associated with each link in the Link Set, and links with
   insufficient link quality are considered lost.  Modifying the link
   quality of a link is OPTIONAL.  If link quality is not to be modified
   it MUST be set to indicate an always usable quality link.  Link
   quality information is only used locally, it is not used in
   signaling, and nodes may interoperate whether they are using the
   same, different, or no, link quality information.

4.3.  Signaling Overview

   Signaling consists of a single type of message, known as a HELLO
   message.  Each node generates HELLO messages for each of its MANET
   interfaces.  Each HELLO message identifies that MANET interface, and
   reports the other interfaces of the node.  Each HELLO message
   includes information from the Link Set of the Interface Information
   Base of the MANET interface, and from the Node Information Base of
   the node.

4.3.1.  HELLO Message Generation

   HELLO messages are generated by a node for each of its MANET
   interfaces, and MAY be sent:

   o  Proactively, at a regular interval, known as HELLO_INTERVAL.
      HELLO_INTERVAL may be fixed, or may be dynamic.  For example
      HELLO_INTERVAL may be backed off due to congestion or network
      stability.

   o  As a response to a change in the node itself, or its 1-hop
      neighborhood, for example on first becoming active or in response
      to a new, broken, or changed status link.

   o  In a combination of these proactive and responsive mechanisms.

   Jittering of HELLO message generation and transmission, as described



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   in Section 11.2, MAY be used if appropriate.

   HELLO messages are generated independently on each MANET interface of
   a node.  HELLO messages MAY be scheduled independently for each MANET
   interface, or, interface parameters permitting, using the same
   schedule for all MANET interfaces of a node.

4.3.2.  HELLO Message Content

   Each HELLO message sent over a MANET interface need not contain all
   of the information appropriate to that MANET interface, however:

   o  A HELLO message MUST contain all of the addresses in the Local
      Interface Set of the node to which the MANET interface belongs.

   o  Within every time interval of length REFRESH_INTERVAL, the HELLO
      messages sent on each MANET interface of a node must collectively
      include:

      *  All of the information in the Link Set of the Interface
         Information Base of that MANET interface (other than link
         quality and information relating to pending links).

      *  All of the information in the Node Information Base of that
         node.

      This applies to otherwise purely responsive nodes as well as
      proactive nodes.  In either case it means that all information
      appropriate to that MANET interface will have always been
      transmitted, in one or more HELLO messages, since the time
      REFRESH_INTERVAL ago.

   o  A HELLO message MUST include a VALIDITY_TIME message TLV that
      indicates the length of time for which the message content is to
      be considered valid, and included in the receiving node's
      Interface Information Base.

   o  A periodically generated HELLO message SHOULD include an
      INTERVAL_TIME message TLV that indicates the current value of
      HELLO_INTERVAL for that MANET interface, i.e. the period within
      which a further HELLO message is guaranteed to be sent on that
      MANET interface.









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5.  Protocol Parameters and Constants

   The parameters and constants used in this specification are described
   in this section.

5.1.  Interface Parameters

   The interface parameters used by this specification may be classified
   into the following four categories:

   o  Message intervals

   o  Information validity times

   o  Link quality

   o  Jitter

   These are detailed in the following sections.

   Different MANET interfaces (on the same or on different nodes) MAY
   employ different interface parameter values, and may change their
   interface parameter values dynamically, subject to the constraints
   given in this section.  A particular case is where all MANET
   interfaces on all MANET nodes within a given MANET employ the same
   set of interface parameter values.

5.1.1.  Message Intervals

   The following interface parameters regulate HELLO message
   transmissions over a given MANET interface.

   HELLO messages serve two principal functions:

   o  To advertise this nodes own addresses to its 1-hop neighbors.  The
      frequency of these advertisements is regulated by the interface
      parameters HELLO_INTERVAL and HELLO_MIN_INTERVAL.

   o  To advertise this nodes knowledge of each of its 1-hop neighbors.
      The frequency of the advertisement of each such neighbor is
      regulated by the interface parameter REFRESH_INTERVAL.

   Specifically, these parameters are as follows:

   HELLO_INTERVAL  - is the maximum time between the transmission of two
      successive HELLO messages on this MANET interface.  If using
      periodic transmission of HELLO messages, these SHOULD be at a
      separation of HELLO_INTERVAL, possibly modified by jitter as



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      specified in [4].

   HELLO_MIN_INTERVAL  - is the minimum interval between transmission of
      two successive HELLO messages, on this MANET interface.  (This
      minimum interval MAY be modified by jitter, as defined in [4].)

   REFRESH_INTERVAL  - is the maximum interval between advertisements in
      a HELLO message of each 1-hop neighbor address and its status.  In
      all intervals of length REFRESH_INTERVAL, a node MUST include all
      1-hop neighbor information which it is specified as sending in at
      least one HELLO message on this MANET interface.

   The following constraints apply to these interface parameters:

   o  HELLO_INTERVAL > 0

   o  HELLO_MIN_INTERVAL >= 0

   o  HELLO_INTERVAL >= HELLO_MIN_INTERVAL

   o  REFRESH_INTERVAL >= HELLO_INTERVAL

   o  If INTERVAL_TIME TLVs as defined in [3] are included in HELLO
      messages, then HELLO_INTERVAL MUST be representable as described
      in [3].

   If REFRESH_INTERVAL > HELLO_INTERVAL, then a node may distribute its
   neighbor advertisements between HELLO messages in any manner, subject
   to the constraints above.

   For a node to employ this protocol in a purely responsive manner on a
   MANET interface, REFRESH_INTERVAL and HELLO_INTERVAL SHOULD both be
   set to a value such that a responsive HELLO message is always
   expected in a shorter period than this.

5.1.2.  Information Validity Times

   The following interface parameters manage the validity time of link
   information:

   L_HOLD_TIME  - is the period of advertisement, on this MANET
      interface, of former 1-hop neighbor addresses as lost in HELLO
      messages, allowing recipients of these HELLO messages to
      accelerate removal of information from their Link Sets.
      L_HOLD_TIME can be set to zero if accelerated information removal
      is not required.





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   H_HOLD_TIME  - is used as the value in the VALIDITY_TIME TLV included
      in all HELLO messages on this MANET interface.

   The following constraints apply to these interface parameters:

   o  L_HOLD_TIME >= 0

   o  H_HOLD_TIME >= REFRESH_INTERVAL

   o  If HELLO messages can be lost then both SHOULD be significantly
      greater than REFRESH_INTERVAL.

   o  H_HOLD_TIME MUST be representable as described in [3].

5.1.3.  Link Quality

   The following interface parameters manage the usage of link quality:

   HYST_ACCEPT  - is the link quality threshold at or above which a link
      becomes usable, if it was not already so.

   HYST_REJECT  - is the link quality threshold below which a link
      becomes unusable, if it was not already so.

   INITIAL_QUALITY  - is the initial quality of a newly identified link.

   INITIAL_PENDING  - if true, then a newly identified link is
      considered pending, and is not usable until the link quality has
      reached or exceeded the HYST_ACCEPT threshold.

   The following constraints apply to these interface parameters:

   o  0 <= HYST_REJECT <= HYST_ACCEPT <= 1

   o  0 <= INITIAL_QUALITY <= 1.

   o  If link quality is not updated, then INITIAL_QUALITY >=
      HYST_ACCEPT.

   o  If INITIAL_QUALITY >= HYST_ACCEPT, then INITIAL_PENDING == false.

   o  If INITIAL_QUALITY < HYST_REJECT, then INITIAL_PENDING == true.

5.1.4.  Jitter

   If jitter, as defined in [4], is used then these parameters are as
   follows:




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   HP_MAXJITTER  - represents the value of MAXJITTER used in [4] for
      periodically generated HELLO messages on this MANET interface.

   HT_MAXJITTER  - represents the value of MAXJITTER used in [4] for
      externally triggered HELLO messages on this MANET interface.

   For constraints on these interface parameters see [4].

5.2.  Node Parameters

   Only one node parameter is defined by this specification, in the
   category of information validity time.

5.2.1.  Information Validity Time

   The following node parameter manages the validity time of lost
   symmetric 1-hop neighbor information:

   N_HOLD_TIME  - is used as the period during which former 1-hop
      neighbor addresses are advertised as lost in HELLO messages,
      allowing recipients of these HELLO messages to accelerate removal
      of information from their 2-Hop Sets.  N_HOLD_TIME can be set to
      zero if accelerated information removal is not required.

   The following constraint applies to this node parameter:

   o  N_HOLD_TIME >= 0

5.3.  Parameter Change Constraints

   This section presents guidelines, applicable if protocol parameters
   are changed dynamically.

   HELLO_INTERVAL

      *  If the HELLO_INTERVAL for a MANET interface increases, then the
         next HELLO message on this MANET interface MUST be generated
         according to the previous, shorter, HELLO_INTERVAL.  Additional
         subsequent HELLO messages MAY be generated according to the
         previous, shorter, HELLO_INTERVAL.

      *  If the HELLO_INTERVAL for a MANET interface decreases, then the
         following HELLO messages on this MANET interface SHOULD be
         generated according to this current, shorter, HELLO_INTERVAL.







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   REFRESH_INTERVAL

      *  If the REFRESH_INTERVAL for a MANET interface increases, then
         the content of subsequent HELLO messages must be organized such
         that the specification of the old value of REFRESH_INTERVAL is
         satisfied for a further period equal to the old value of
         REFRESH_INTERVAL.

      *  If the REFRESH_INTERVAL for a MANET interface decreases, then
         it MAY be necessary to reschedule HELLO message generation on
         that MANET interface, in order that the specification of
         REFRESH_INTERVAL is satisfied from the time of change.

   HYST_ACCEPT and HYST_REJECT

      *  If HYST_ACCEPT or HYST_REJECT changes, then the appropriate
         actions for link quality change, as specified in Section 14.3
         MUST be taken.

   L_HOLD_TIME

      *  If L_HOLD_TIME changes, then L_time for all relevant Link
         Tuples SHOULD be changed.

   N_HOLD_TIME

      *  If N_HOLD_TIME changes, then NL_time for all relevant Lost
         Neighbor Tuples SHOULD be changed.

   HP_MAXJITTER

      *  If HP_MAXJITTER changes, then the periodic HELLO message
         schedule on this MANET interface MAY be changed.

   HT_MAXJITTER

      *  If HT_MAXJITTER changes, then externally triggered HELLO
         messages on this MANET interface MAY be rescheduled.

5.4.  Constants

   The constant C is used as specified in [3].









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6.  Local Information Base

   A node maintains a Local Information Base that records information
   about its local interfaces (MANET interfaces or otherwise).  Each
   such interface MUST have at least one address, and MAY have more than
   one address.  All addresses have an associated prefix length, which
   is included with all addresses in the Local Information Base.  If an
   address otherwise does not have a prefix length then it is considered
   to be equal to the address length.  Two addresses are considered
   equal if and only if their associated prefix lengths are also equal.

   The Local Information Base is not modified by this protocol.  This
   protocol MAY respond to changes of this Local Information Base which
   MUST reflect corresponding changes in the node's interface
   configuration.

6.1.  Local Interface Set

   A node's Local Interface Set records its local interfaces.  It
   consists of Local Interface Tuples, one per interface:

      (I_local_iface_addr_list, I_manet)

   where:

   I_local_iface_addr_list  is a list of the addresses of this
      interface.

   I_manet  is a boolean flag, describing if this interface is a MANET
      interface.





















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7.  Interface Information Base

   A node maintains an Interface Information Base for each of its MANET
   interfaces.  This records information about links to that MANET
   interface and symmetric 2-hop neighbors which can be reached in two
   hops using those links as the first hop.  The Interface Information
   Base includes the Link Set and the 2-Hop Set.

   A MANET interface address can be present in both the Link Set and as
   of a symmetric 2-hop neighbor.  This allows the node with this MANET
   interface address to be immediately considered as a symmetric 2-hop
   neighbor if it fails to be a symmetric 1-hop neighbor.

   All addresses MUST have an associated prefix length, which is
   included in all addresses in the Interface Information Base.  Prefix
   lengths are indicated in HELLO messages using the PREFIX_LENGTH TLV
   specified in [1]; if an address has no such TLV, then its prefix
   length is equal to the address length.  Two addresses are considered
   equal if and only if their associated prefix lengths are also equal.

7.1.  Link Set

   A node's Link Set records links from other nodes which are, or
   recently were, 1-hop neighbors.  It consists of Link Tuples, each
   representing a single link:

      (L_neighbor_iface_addr_list, L_HEARD_time,
       L_SYM_time, L_quality, L_pending, L_lost, L_time)

   where:

   L_neighbor_iface_addr_list  is a list of the addresses of the MANET
      interface of the 1-hop neighbor;

   L_HEARD_time  is the time until which the MANET interface of the
      1-hop neighbor would be considered heard if not considering link
      quality;

   L_SYM_time  is the time until which the link to the 1-hop neighbor
      would be considered symmetric if not considering link quality;

   L_quality  is a dimensionless number between 0 (inclusive) and 1
      (inclusive) describing the quality of a link; a greater value of
      L_quality indicating a higher quality link;







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   L_pending  is a boolean flag, describing if a link is considered
      pending (i.e. a candidate, but not yet established, link);

   L_lost  is a boolean flag, describing if a link is considered lost
      due to link quality;

   L_time  specifies when this Tuple expires and MUST be removed.

   The status of the link, as obtained through HELLO message exchange,
   and also taking link quality into account, denoted L_status, is
   defined by:

   1.  If L_pending is true, then L_status = PENDING;

   2.  otherwise, if L_lost is true, then L_status = LOST;

   3.  otherwise, if L_SYM_time is not expired, then L_status =
       SYMMETRIC;

   4.  otherwise, if L_HEARD_time is not expired, then L_status = HEARD;

   5.  otherwise, L_status = LOST.

7.2.  2-Hop  Set

   A node's 2-Hop Set records symmetric 2-hop neighbors, and the
   symmetric links to symmetric 1-hop neighbors through which the
   symmetric 2-hop neighbors can be reached.  It consists of 2-Hop
   Tuples, each representing a single interface address of a symmetric
   2-hop neighbor, and a single MANET interface of a symmetric 1-hop
   neighbor.

      (N2_neighbor_iface_addr_list, N2_2hop_iface_addr, N2_time)

   where:

   N2_neighbor_iface_addr_list  is a list of the addresses of the MANET
      interface of the symmetric 1-hop neighbor from which this
      information was received;

   N2_2hop_iface_addr  is an address of an interface of a symmetric
      2-hop neighbor which has a symmetric link (using any MANET
      interface) to the indicated symmetric 1-hop neighbor;

   N2_time  specifies when this Tuple expires and MUST be removed.






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8.  Node Information Base

   Each node maintains a Node Information Base that records information
   about addresses of current and recently symmetric 1-hop neighbors.

   All addresses MUST have an associated prefix length, which is
   included in all addresses in the Node Information Base.  Prefix
   lengths are indicated in HELLO messages using the PREFIX_LENGTH TLV
   specified in [1]; if an address has no such TLV, then its prefix
   length is equal to the address length.  Two addresses are considered
   equal if and only if their associated prefix lengths are also equal.

8.1.  Neighbor Set

   A node's Neighbor Set records all interface addresses of each 1-hop
   neighbor.  It consists of Neighbor Tuples, each representing a single
   1-hop neighbor:

      (N_neighbor_iface_addr_list, N_symmetric)

   where:

   N_neighbor_iface_addr_list  is a list of the interface addresses of a
      1-hop neighbor;

   N_symmetric  is a boolean flag, describing if this is a symmetric
      1-hop neighbor.

8.2.  Lost Neighbor Set

   A node's Lost Neighbor Set records addresses of all interfaces of
   nodes which recently were symmetric 1-hop neighbors, but are now
   advertised as lost.  It consists of Lost Neighbor Tuples, each
   representing a single such address:

      (NL_neighbor_iface_addr, NL_time)

   where:

   NL_neighbor_iface_addr  is an address of an interface of a node which
      recently was a symmetric 1-hop neighbor of this node;

   NL_time  specifies when this Tuple expires and MUST be removed.








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9.  Local Information Base Changes

   The Local Information Base MUST change to respond to changes in the
   node's interfaces.  The node MUST update its Interface and Node
   Information Bases in response to such changes.  If any changes in the
   Interface and Node Information Bases satisfy any of the conditions
   described in Section 13, then those changes must be applied
   immediately, unless noted otherwise.

   A node MAY transmit HELLO messages in response to these changes.

9.1.  Adding an Interface

   If an interface is added to the node then this is indicated by the
   addition of a Local Interface Tuple to the Local Interface Set. If
   the new interface is a MANET interface then an initially empty
   Interface Information Base MUST be created for this new MANET
   interface.  The actions in Section 9.3 MUST be taken for each address
   of the added interface.  A HELLO message MAY be sent on all MANET
   interfaces, it SHOULD be sent on the new interface if it is a MANET
   interface.  If using scheduled messages, then a message schedule MUST
   be established on a new MANET interface.

9.2.  Removing an Interface

   If a MANET interface is removed from the node, then this MUST result
   in removal of information from the Local Information Base and the
   Neighborhood Information Base as follows:

   1.  Remove the Local Interface Tuple that corresponds to the
       interface to be removed from the Local Interface Set.

   2.  If the interface to be removed is a MANET interface (i.e. with
       I_manet == true) then:

       1.  Remove the Interface Information Base for that MANET
           interface;

       2.  All Neighbor Tuples for which none of the addresses in its
           N_neighbor_iface_addr_list are found in any
           L_neighbor_iface_addr_list in any remaining Link Set, are
           removed.

   If a node removes the Local Interface Tuple that contains the
   interface address that is used to define the node's originator
   address, as defined in [1], then the node MAY change originator
   address.




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   If the removed interface is the last MANET interface of the node,
   then there will be no remaining Interface Information Bases, and the
   node will longer participate in this protocol.

   A HELLO message MAY be sent on all remaining MANET interfaces.

9.3.  Adding an Address to an Interface

   If an address is added to an interface then this is indicated by the
   addition of an address to the appropriate I_local_iface_addr_list.
   The following changes MUST be made to the Information Bases:

   1.  The Neighbor Tuples, if any, whose N_neighbor_iface_addr_list
       contains the added address, are removed.

   2.  Any Link Tuples, in any Link Set, whose
       L_neighbor_iface_addr_list contains:

       *  the added address; OR

       *  any address in the N_neighbor_iface_addr_list of the removed
          Neighbor Tuples, if any

       are removed; apply Section 13.1, but not Section 13.3.

   3.  Any Lost Neighbor Tuples whose NL_neighb_iface_addr is the added
       address, are removed.

   4.  Any 2-Hop Tuples whose N2_2hop_iface_addr is the added address,
       are removed.

   A HELLO message MAY be sent on all MANET interfaces.

9.4.  Removing an Address from an Interface

   If an address is removed from an interface then this is indicated by
   the removal of an address from the appropriate
   I_local_iface_addr_list.  If this list is now empty then the
   corresponding Local Interface Tuple MUST be removed.

   If a node removes the interface address that is used to define the
   node's originator address, as defined in [1], then the node MAY
   change originator address.

   A HELLO message MAY be sent on all MANET interfaces.






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10.  Packets and Messages

   The packet and message format used by this protocol is defined in
   [1], which is used with the following considerations:

   o  This protocol specifies one message type, the HELLO message.

   o  HELLO message header options MAY be used as specified by a
      protocol which uses this neighborhood discovery protocol.

   o  HELLO messages MUST NOT be forwarded.

   o  HELLO messages MAY be included in multi-message packets as
      specified in [1].

   o  Packet header options MAY be used as specified by a protocol which
      uses this neighborhood discovery protocol.

   o  This protocol specifies three address block TLVs.  It also uses
      two message TLVs defined in [3] and one address block TLV defined
      in [1].  These six TLV types are all defined only with Subtype ==
      0.  TLVs of other types, and of these types but without Subtype ==
      0, are ignored by this protocol.  All references in this protocol
      to, for example, a TLV with Type == LINK_STATUS, are to be
      considered as referring to a TLV with Type == LINK_STATUS and
      Subtype == 0.

10.1.  HELLO Messages

   A HELLO message MUST contain:

   o  A VALIDITY_TIME message TLV as specified in [3], representing
      H_HOLD_TIME for the transmitting MANET interface.

   o  An address block, with an associated TLV block, known as the Local
      Interface Block, as specified in Section 10.1.1.

   A HELLO message which is transmitted periodically SHOULD contain, and
   otherwise MAY contain:

   o  An INTERVAL_TIME message TLV as specified in [3], representing
      HELLO_INTERVAL for the transmitting MANET interface.

   A HELLO message MAY contain:

   o  One or more address blocks, each with an associated TLV block,
      known as Neighbor Address Blocks, as specified in Section 10.1.2.




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   o  Other message TLVs.

10.1.1.  Local Interface Block

   The first address block, plus following TLV block, in a HELLO message
   is known as the Local Interface Block.  The Local Interface Block is
   not distinguished in any way other than by being the first address
   block in the HELLO message.

   The Local Interface Block MUST contain all of the addresses in that
   node's Local Interface Set. Those addresses, if any, which correspond
   to interfaces other than the MANET interface for which the HELLO
   message is transmitted MUST be associated with a corresponding TLV
   with Type == OTHER_IF as specified in Table 1.  Addresses of the
   MANET interface on which the HELLO message is transmitted MUST NOT be
   associated with such a TLV.

   Note that a Local Interface Block MAY include more than one address
   for each MANET interface, and hence a HELLO message MAY contain more
   than one address without an OTHER_IF TLV.

   +----------+--------+-----------------------------------------------+
   |   Name   |  Value | Description                                   |
   |          | Length |                                               |
   +----------+--------+-----------------------------------------------+
   | OTHER_IF | 0 bits | Specifies that the address, in the Local      |
   |          |        | Interface Block of the message, is an address |
   |          |        | associated with an interface other than the   |
   |          |        | MANET interface on which the message is       |
   |          |        | transmitted                                   |
   +----------+--------+-----------------------------------------------+

                                  Table 1

10.1.2.  Neighbor Address Blocks

   Address blocks, each with a following TLV block, in a HELLO message,
   after the Local Interface Block, are known as Neighbor Address
   Blocks.  These Neighbor Address Blocks are not distinguished in any
   way other than by not being the first address block in the HELLO
   message.  A HELLO message MAY contain no Neighbor Address Blocks.

   A Neighbor Address Block contains current or recently lost 1-hop
   neighbors' interface addresses, each of which is associated with
   address block TLVs as described in Table 2.  Other addresses MAY be
   included in Neighbor Address Blocks, but MUST NOT be associated with
   any of the TLVs specified in Table 2.




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   +--------------+--------+-------------------------------------------+
   |     Name     |  Value | Description                               |
   |              | Length |                                           |
   +--------------+--------+-------------------------------------------+
   |  LINK_STATUS | 8 bits | Specifies the status of the link from the |
   |              |        | indicated address (LOST, SYMMETRIC or     |
   |              |        | HEARD)                                    |
   |              |        |                                           |
   | OTHER_NEIGHB | 8 bits | Specifies that the address is (SYMMETRIC) |
   |              |        | or was (LOST) of an interface of a        |
   |              |        | symmetric 1-hop neighbor of the node      |
   |              |        | transmitting the HELLO message            |
   +--------------+--------+-------------------------------------------+

                                  Table 2

   A TLV with Type == LINK_STATUS and (Value == SYMMETRIC or Value ==
   LOST) also performs the function of a TLV with Type == OTHER_IF and
   the same value.  The latter SHOULD NOT also be included.  If a TLV
   with Type == LINK_STATUS and Value == SYMMETRIC is combined with a
   TLV with Type == OTHER_IF and Value == LOST then the latter MUST be
   ignored, and SHOULD NOT be included.  See Appendix A.





























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11.  HELLO Message Generation

   Each MANET interface MUST generate HELLO messages according to the
   specification in this section.  HELLO message generation and
   scheduling MUST be according to the interface parameters for that
   MANET interface and MAY be independent for each MANET interface or,
   interface parameters permitting, MANET interfaces MAY use the same
   schedule.

   If transmitting periodic HELLO messages then, following a HELLO
   message transmission on a MANET interface, another HELLO message MUST
   be transmitted on the same MANET interface after an interval not
   greater than HELLO_INTERVAL.  Two successive HELLO message
   transmissions on the same MANET interface MUST be separated by at
   least HELLO_MIN_INTERVAL, except as noted in Section 11.2.1.

11.1.  HELLO Message Specification

   HELLO messages are generated independently on each MANET interface.

   A HELLO message MUST include a Local Interface Block, as specified in
   Section 10.1.1, as its first address block.

   Other addresses which MUST be included in Neighbor Address Blocks, as
   specified in Section 10.1.2, in HELLO messages sent over a given
   MANET interface are:

   o  Addresses of MANET interfaces of 1-hop neighbors from the Link Set
      of the Interface Information Base for this MANET interface.

   o  Other addresses of symmetric 1-hop neighbors from the Neighbor Set
      of this node's Node Information Base.

   o  Addresses of MANET interfaces of previously symmetric or heard
      1-hop neighbors connected on this MANET interface from the Link
      Set of the Interface Information Base for this MANET interface.
      (These are advertised for a period equal to this interface's
      L_HOLD_TIME after loss.)

   o  Other addresses of previously symmetric 1-hop neighbors from the
      Lost Neighbor Set of this node's Node Information Base.  (These
      are advertised for a period equal to N_HOLD_TIME after loss.)

   The addresses, and their associated TLVs, which may be included in
   any HELLO message sent on this MANET interface (respecting
   REFRESH_INTERVAL for this MANET interface) are:





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   1.  For each address (henceforth linked address) which appears in a
       Link Tuple in the Link Set for this MANET interface, for which
       L_status does not equal PENDING, include the linked address with
       an associated TLV with:

       *  Type = LINK_STATUS; AND

       *  Value = L_status.

   2.  For each address (henceforth neighbor address) which appears in
       an N_neighbor_iface_addr_list in a Neighbor Tuple with
       N_symmetric == true, and which has not already been included with
       an associated TLV with (Type == LINK_STATUS and Value ==
       SYMMETRIC), include the neighbor address with an associated TLV
       with:

       *  Type = OTHER_NEIGHB; AND

       *  Value = SYMMETRIC.

   3.  For each Lost Neighbor Tuple whose NL_neighbor_iface_addr
       (henceforth lost address) has not already been included, include
       the lost address with an associated TLV with:

       *  Type = OTHER_NEIGHB; AND

       *  Value = LOST.

   If an address is specified with more than one associated TLV, then
   these TLVs MAY be independently included or excluded from each HELLO
   message.  Each such TLV MUST be included associated with that address
   in a HELLO message sent on that MANET interface in every interval of
   length equal to that MANET interface's parameter REFRESH_INTERVAL.
   TLVs associated with the same address included in the same HELLO
   message MAY be applied to the same or different copies of that
   address.

11.2.  HELLO Message Transmission

   HELLO messages are transmitted in the packet/message format specified
   by [1] using the "LL MANET Routers" multicast address specified by
   [2] as destination IP address, using the MANET UDP port specified in
   [2].

11.2.1.  HELLO Message Jitter

   HELLO messages MAY be sent using periodic message generation or
   externally triggered message generation.  If using data link and



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   physical layers which are subject to packet loss due to collisions,
   HELLO messages SHOULD be jittered as described in [4].

   Internally triggered message generation (such as due to a change in
   local interfaces) MAY be treated as if externally generated message
   generation, or MAY be not jittered.

   HELLO messages MUST NOT be forwarded, and thus message forwarding
   jitter does not apply to HELLO messages.

   Each form of jitter described in [4] requires a parameter MAXJITTER.
   These interface parameters may be dynamic, and are specified by:

   o  For periodic message generation: HP_MAXJITTER, which MUST be
      significantly less than HELLO_INTERVAL.

   o  For externally triggered message generation: HT_MAXJITTER.  If
      HELLO messages are also periodically generated, then HT_MAXJITTER
      also MUST be significantly less than HELLO_INTERVAL.

   When HELLO message generation is delayed in order that a HELLO
   message is not sent within HELLO_MIN_INTERVAL of the previous HELLO
   message on the same MANET interface, then HELLO_MIN_INTERVAL SHOULD
   be reduced by jitter, with maximum reduction HP_MAXJITTER.  In this
   case HP_MAXJITTER MUST NOT be greater than HELLO_MIN_INTERVAL.


























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12.  HELLO Message Processing

   On receiving a HELLO message, a node MUST first check if any address
   in its Local Interface Block is one of its interface addresses (i.e.
   is in any I_local_iface_addr_list in the Local Interface Set).  If so
   then the HELLO message MUST be discarded.

   Otherwise the receiving node MUST update its appropriate Interface
   Information Base and its Node Information Base according to this
   section.  If any changes satisfy any of the conditions described in
   Section 13 then the indicated consequences MUST be applied
   immediately, unless noted otherwise.

   For the purpose of this section, note the following definitions:

   o  "validity time" is calculated from the VALIDITY_TIME TLV of the
      HELLO message as specified in [3].

   o  "Receiving Address List" is the I_local_iface_addr_list
      corresponding to the MANET interface on which the HELLO message
      was received

   o  "Neighbor Address List" is the list of the addresses contained in
      the Local Interface Block of the HELLO message.

   o  "Sending Address List" is the list of the addresses contained in
      the Local Interface Block of the HELLO message which do not have
      an associated TLV with Type == OTHER_IF.

   o  EXPIRED indicates that a timer is set to a value clearly preceding
      the current time (e.g. current time - 1).

   o  "Removed Address List" is a list of addresses created by this
      HELLO message processing which were formerly reported as local by
      the node originating the HELLO message, but which are not included
      in the Neighbor Address List.  This list is initialized as empty.

   o  "Lost Address List" is a subset of the Removed Address List
      containing addresses which were formerly considered as symmetric.
      This list is initialized as empty.

12.1.  Updating the Neighbor Set

   On receiving a HELLO message, the node MUST update its Neighbor Set
   and populate the Removed Address List and Lost Address List:

   1.  Find all Neighbor Tuples (hereafter matching Neighbor Tuples)
       where:



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       *  N_neighbor_iface_addr_list contains at least one address in
          the Neighbor Address List.

   2.  If there are no matching Neighbor Tuples, then:

       1.  Create a new Neighbor Tuple with:

           +  N_neighbor_iface_addr_list = Neighbor Address List;

           +  N_symmetric = false.

   3.  If there is one matching Neighbor Tuple, then:

       1.  If the N_neighbor_iface_addr_list of the matching Neighbor
           Tuple is not equal to the Neighbor Address List, then:

           1.  For each address (henceforth removed address) which is in
               the N_neighbor_iface_addr_list, but not in the Neighbor
               Address List:

               1.  Add the removed address to the Removed Address List.

               2.  If N_symmetric == true, then add the removed address
                   to the Lost Address List.

           2.  Update the matching Neighbor Tuple by:

               -  N_neighbor_iface_addr_list = Neighbor Address List.

   4.  If there are two or more matching Neighbor Tuples, then:

       1.  For each address (henceforth removed address) which is in the
           N_neighbor_iface_addr_list of any of the matching Neighbor
           Tuples:

           1.  Add the removed address to the Removed Address List.

           2.  If N_symmetric == true, then add the removed address to
               the Lost Address List.

       2.  Replace the matching Neighbor Tuples by a single Neighbor
           Tuple with:

           +  N_neighbor_iface_addr_list = Neighbor Address List;

           +  N_symmetric = false





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12.2.  Updating the Lost Neighbor Set

   On receiving a HELLO message, a node MUST update its Lost Neighbor
   Set:

   1.  For each address (henceforth lost address) in the Lost Neighbor
       List, if no Lost Neighbor Tuple with NL_neighbor_iface_addr ==
       lost address exists, then add a Lost Neighbor Tuple with:

       *  NL_neighbor_iface_addr = lost address;

       *  NL_time = current time + N_HOLD_TIME.

12.3.  Updating the Link Set

   On receiving a HELLO message, a node MUST update its Link Set for the
   MANET interface on which the HELLO message is received:

   1.  Remove all addresses in the Removed Address List from the
       L_neighbor_iface_addr_list of all Link Tuples.

   2.  Remove all Link Tuples whose L_neighbor_iface_addr_list is now
       empty; apply Section 13.1, but not Section 13.3.

   3.  Find all Link Tuples (hereafter matching Link Tuples) where:

       *  L_neighbor_iface_addr_list contains one or more addresses in
          the Sending Address List.

   4.  If there is more than one matching Link Tuple, then remove them
       all; apply Section 13.1, but not Section 13.3.

   5.  If no matching Link Tuples remain, then create a new matching
       Link Tuple with:

       *  L_neighbor_iface_addr_list = empty;

       *  L_HEARD_time = EXPIRED;

       *  L_SYM_time = EXPIRED;

       *  L_quality = INITIAL_QUALITY;

       *  L_pending = INITIAL_PENDING;

       *  L_lost = false;





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       *  L_time = current time + validity time.

   6.  The matching Link Tuple, existing or new, is then modified as
       follows:

       1.  If the MANET interface finds any address (henceforth
           receiving address) in the Receiving Address List in a
           Neighbor Address Block in the HELLO message, then the Link
           Tuple is modified as follows:

           1.  If any receiving address in the HELLO message is
               associated with a TLV with Type == LINK_STATUS and (Value
               == HEARD or Value == SYMMETRIC) then:

               -  L_SYM_time = current time + validity time.

           2.  Otherwise if any receiving address in the HELLO message
               is associated with a TLV with Type == LINK_STATUS and
               Value == LOST then:

               1.  if L_SYM_time has not expired, then:

                   1.  L_SYM_time = EXPIRED.

                   2.  if L_status == HEARD or SYMMETRIC, then:

                       *  L_time = current time + L_HOLD_TIME.

       2.  L_neighbor_iface_addr_list = Sending Address List.

       3.  L_HEARD_time = max(current time + validity time, L_SYM_time).

       4.  If L_status == PENDING, then:

           +  L_time = max(L_time, L_HEARD_time).

       5.  Otherwise if L_status == HEARD or SYMMETRIC, then:

           +  L_time = max(L_time, L_HEARD_time + L_HOLD_TIME).

12.4.  Updating the 2-Hop Set

   On receiving a HELLO message a node MUST update its 2-Hop Set for the
   MANET interface on which the HELLO message was received:

   1.  Remove all addresses in the Removed Address List from the
       N2_neighbor_iface_addr_list of all 2-Hop Tuples.




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   2.  If the Link Tuple with L_neighbor_iface_addr_list == Sending
       Address List has L_STATUS == SYMMETRIC then:

       1.  For each address (henceforth 2-hop address) in a Neighbor
           Address Block of the HELLO message, which is not in the
           Neighbor Address List or in any I_local_iface_addr_list:

           1.  If the 2-hop address has an associated TLV with:

               -  Type == LINK_STATUS and Value == SYMMETRIC; OR

               -  Type == OTHER_NEIGHB and Value == SYMMETRIC,

               then, if there is no 2-Hop Tuple such that:

               -  N2_neighbor_iface_addr_list contains one or more
                  addresses in the Sending Address List; AND

               -  N2_2hop_iface_addr == 2-hop address.

               then create a 2-Hop Neighbor Tuple with:

               -  N2_2hop_iface_addr = 2-hop address.

               This 2-Hop Tuple (existing or new) is then modified as
               follows:

               -  N2_neighbor_iface_addr_list = Sending Address List;

               -  N2_time = current time + validity time.

           2.  Otherwise if the 2-hop address has a TLV with:

               -  Type == LINK_STATUS and (Value == LOST or Value ==
                  HEARD); OR

               -  Type == OTHER_NEIGHB and Value == LOST;

               then remove all 2-Hop Tuples with:

               -  N2_neighbor_iface_addr_list contains one or more
                  addresses in the Sending Address List; AND

               -  N2_2hop_iface_addr == 2-hop address.







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13.  Other Information Base Changes

   The Interface and Node Information Bases MUST be changed when some
   events occur.  These events may result from HELLO message processing,
   or may be otherwise generated (e.g. expiry of timers or link quality
   changes).

   Events which cause changes in the Information Bases are:

   o  A Link Tuple's state changes from symmetric, or the Link Tuple is
      removed.

   o  A Link Tuple's state changes to symmetric.

   o  A Link Tuple's L_HEARD_time expires, or the Link Tuple is removed.

   o  Local interface address changes, as specified in Section 9.

   o  Link quality changes, as specified in Section 14.

   A node MAY report updated information in response to any of these
   changes in HELLO message(s), subject to the constraints in
   Section 11.

   A node which transmits HELLO messages in response to such changes
   SHOULD transmit a HELLO message:

   o  On all MANET interfaces, if the Neighbor Set changes such as to
      indicate the change in symmetry of any 1-hop neighbors (including
      addition or removal of symmetric 1-hop neighbors).

   o  Otherwise, on all those MANET interfaces whose Link Set changes
      such as to indicate a change in status of any 1-hop neighbors
      (including the addition or removal of any 1-hop neighbors, other
      than those considered pending).

13.1.  Link Tuple Not Symmetric

   If for any Link Tuple with L_status == SYMMETRIC:

   o  L_status changes to any other value; OR

   o  the Link Tuple is removed;

   then:

   1.  All 2-Hop Tuples for the same MANET interface with:




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       *  N2_neighbor_iface_addr_list contains one or more addresses in
          L_neighbor_iface_addr_list;

       are removed.

   2.  For the Neighbor Tuple whose N_neighbor_iface_addr_list contains
       L_neighbor_iface_addr_list:

       1.  If there are no remaining Link Tuples for any MANET interface
           with:

           +  L_neighbor_iface_addr_list contained in
              N_neighbor_iface_addr_list; AND

           +  L_status == SYMMETRIC;

           then modify the Neighbor Tuple by:

           1.  N_symmetric = false.

           2.  For each address (henceforth neighbor address) in
               N_neighbor_iface_addr_list, add a Lost Neighbor Tuple
               with:

               -  NL_neighbor_iface_addr = neighbor address;

               -  NL_time = current time + N_HOLD_TIME.

13.2.  Link Tuple Symmetric

   If, for any Link Tuple which does not have L_status == SYMMETRIC:

   o  L_status changes to SYMMETRIC;

   (this includes a newly created Link Tuple which is immediately
   updated to have L_status == SYMMETRIC) then:

   1.  For the Neighbor Tuple whose N_neighbor_iface_addr_list includes
       L_neighbor_iface_addr_list, set:

       *  N_symmetric = true.

   2.  Remove all Lost Neighbor Tuples whose LN_neighbor_iface_addr is
       included in that N_neighbor_iface_addr_list.







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13.3.  Link Tuple Heard Timeout

   If, for any Link Tuple:

   o  L_HEARD_time expires; OR

   o  the Link Tuple is removed;

   then:

   1.  For the Neighbor Tuple whose N_neighbor_iface_addr_list contains
       L_neighbor_iface_addr_list, if no Link Tuples for any MANET
       interface remain with:

       *  L_neighbor_iface_addr_list contained in
          N_neighbor_iface_addr_list;

       *  L_HEARD_time is not expired;

       then remove the Neighbor Tuple.































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14.  Link Quality

   Link quality is a mechanism whereby a node MAY take considerations
   other than message exchange into account for determining when a link
   is and is not a candidate for being considered as HEARD or SYMMETRIC.

   For deployments where no link quality is used, the considerations in
   Section 14.1 apply.  For deployments were link quality is used, the
   general principles of link quality usage are described in
   Section 14.2.  Section 14.3 and Section 14.4 detail link quality
   functioning.

   Link quality is used only locally by a node, and nodes may fully
   interoperate whether they are using the same, different or no link
   quality methods.

14.1.  Deployment Without Link Quality

   In order for a node to not employ link quality, the node MUST define:

   o  INITIAL_PENDING = false;

   o  INITIAL_QUALITY >= HYST_REJECT (there is no reason not to define
      INITIAL_QUALITY = 1).

14.2.  Basic Principles of Link Quality

   To enable link quality usage, the L_quality value of a Link Tuple is
   used in conjunction with two thresholds, HYST_ACCEPT and HYST_REJECT,
   to set the flags L_pending and L_lost of that Link Tuple.  Based on
   these flags, the link status to advertise for that Link Tuple is
   determined as described in Section 7.1.

   The use of two thresholds implements link hysteresis, whereby a link
   which has HYST_REJECT <= L_quality < HYST_ACCEPT may be either
   accepted or rejected (depending on which threshold it has most
   recently crossed, or if neither the value of INITIAL_QUALITY).  With
   appropriate values of these parameters, this prevents over-rapid
   changes of link status.

   The basic principles of link quality usage are as follows:

   o  A node does not advertise a neighbor interface in any state until
      L_quality is acceptable:

      *  If INITIAL_PENDING == true, then this is such that L_quality >=
         HYST_ACCEPT.




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      *  Otherwise this is such that L_quality >= HYST_REJECT.  To
         ensure this, a node MUST NOT define INITIAL_PENDING == false
         and INITIAL_QUALITY < HYST_REJECT.  (A node also MUST NOT
         define INITIAL_PENDING == true and INITIAL_QUALITY >=
         HYST_ACCEPT.)

      *  A link which is not yet advertised has L_pending == true.

   o  Once L_quality >= HYST_ACCEPT, the L_pending flag is set false,
      indicating that the link can be advertised.

   o  A link for which L_pending == false is advertised until its
      L_quality drops below HYST_REJECT.

   o  If a link has L_pending == false and L_quality < HYST_REJECT, the
      link is LOST and is advertised as such.  This link is not
      reconsidered as a candidate HEARD or SYMMETRIC link until
      L_quality >= HYST_ACCEPT.

   o  A link which has an acceptable quality may be advertised as HEARD,
      SYMMETRIC or LOST according to the exchange of HELLO messages.

14.3.  When Link Quality Changes

   If L_quality for a link changes, then the following actions MUST be
   taken:

   1.  If L_quality >= HYST_ACCEPT then the corresponding Link Tuple is
       modified by:

       1.  L_pending = false.

       2.  L_lost = false.

       3.  If L_status == HEARD or L_status == SYMMETRIC, then:

           +  L_time = max(L_time, L_HEARD_time + L_HOLD_TIME)

   2.  If L_status is not equal to PENDING, and L_quality < HYST_REJECT
       then the corresponding Link Tuple is modified by:

       1.  If L_lost == false, then:

           +  L_lost = true

           +  L_time = min(L_time, current time + L_HOLD_TIME)

   Any appropriate action indicted in Section 13 MUST also be taken.



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   If L_quality for a link is updated based on HELLO message reception,
   or on reception of a packet including a HELLO message, then L_quality
   MUST be updated prior to the HELLO message processing described in
   Section 12.  (If the receipt of the HELLO message, or the packet
   containing it, creates the Link Tuple then instead the Link Tuple
   MUST be created with the updated, from INITIAL_QUALITY, L_quality
   value.)

14.4.  Updating Link Quality

   A node MAY update link quality based on any information available to
   it.  Particular cases that MAY be used include:

   o  Information from the link layer, such as signal to noise ratio.

   o  Receipt or loss of packets.  If packets include a packet sequence
      number as defined in [1], then packets on a link SHOULD have
      sequential packet sequence numbers, whether or not they include
      HELLO messages.  Link quality can be updated when a packet is
      received based on, for example, whether the last N out of M
      packets on the link were received, or a "leaky integrator"
      tracking packets.

   o  Receipt or loss of HELLO messages.  If the maximum interval
      between HELLO messages is known (such as by inclusion of a message
      TLV with Type == INTERVAL_TIME, as defined in [3], in HELLO
      messages) then the loss of HELLO messages can be determined
      without the need to receive a HELLO message.  Note that if this
      case is combined with the previous case then care must be taken to
      avoid "double counting" a lost HELLO message in a lost packet.





















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15.  Proposed Values for Parameters and Constants

   This section lists the parameters and constants used in the
   specification of the protocol, and proposed values of each which may
   be used when a single value of each is used.

15.1.  Message Interval Interface Parameters

   o  HELLO_INTERVAL = 2 seconds

   o  HELLO_MIN_INTERVAL = HELLO_INTERVAL/4

   o  REFRESH_INTERVAL = HELLO_INTERVAL

15.2.  Information Validity Time Interface Parameters

   o  H_HOLD_TIME = 3 x REFRESH_INTERVAL

   o  L_HOLD_TIME = H_HOLD_TIME

15.3.  Information Validity Time Node Parameters

   o  N_HOLD_TIME = L_HOLD_TIME

15.4.  Link Quality Interface Parameters

   If link quality is changed, then parameter values will depend on the
   link quality process.  If link quality is not changed, then:

   o  HYST_ACCEPT = 1

   o  HYST_REJECT = 0

   o  INITIAL_QUALITY = 1

   o  INITIAL_PENDING = false

15.5.  Jitter Interface Parameters

   o  HP_MAXJITTER = HELLO_INTERVAL/4

   o  HT_MAXJITTER = HP_MAXJITTER

15.6.  Constants

   o  C = 0.0625 second (1/16 second)





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16.  IANA Considerations

16.1.  Message Types

   This specification defines one message type, which must be allocated
   from the "Assigned Message Types" repository of [1] with assignment
   as specified in Table 3.

                    +-------+------+-----------------+
                    |  Name | Type | Description     |
                    +-------+------+-----------------+
                    | HELLO |  TBD | Local signaling |
                    +-------+------+-----------------+

                                  Table 3

16.2.  TLV Types

   This specification defines three address block TLV types, which must
   be allocated from the "Assigned Address Block TLV Types" repository
   of [1] with assignments as specified in Table 4.

   +--------------+------+---------+-----------------------------------+
   |     Name     | Type | Subtype | Description                       |
   +--------------+------+---------+-----------------------------------+
   |   OTHER_IF   |  TBD |    0    | Specifies that the address is     |
   |              |      |         | associated with an interface      |
   |              |      |         | other than the MANET interface on |
   |              |      |         | which the message is transmitted  |
   |              |      |         |                                   |
   |              |      |  1-255  | RESERVED                          |
   |              |      |         |                                   |
   |  LINK_STATUS |  TBD |    0    | Specifies the status of the link  |
   |              |      |         | from the indicated address (LOST, |
   |              |      |         | SYMMETRIC or HEARD)               |
   |              |      |         |                                   |
   |              |      |  1-255  | RESERVED                          |
   |              |      |         |                                   |
   | OTHER_NEIGHB |  TBD |    0    | Specifies that the address is     |
   |              |      |         | (SYMMETRIC) or recently was       |
   |              |      |         | (LOST) of an interface of a       |
   |              |      |         | symmetric 1-hop neighbor of the   |
   |              |      |         | node transmitting the message     |
   |              |      |         |                                   |
   |              |      |  1-255  | RESERVED                          |
   +--------------+------+---------+-----------------------------------+

                                  Table 4



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   Subtypes indicated as RESERVED may be allocated by standards action,
   as specified in [6].

16.3.  LINK_STATUS and OTHER_NEIGHB Values

   The values which the LINK_STATUS TLV can use are the following:

   o  LOST = 0

   o  SYMMETRIC = 1

   o  HEARD = 2

   The values which the OTHER_NEIGHB TLV can use are the following:

   o  LOST = 0

   o  SYMMETRIC = 1

































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17.  References

17.1.  Normative References

   [1]  Clausen, T., Dearlove, C., Dean, J., and C. Adjih, "Generalized
        MANET Packet/Message Format", Work In
        Progress draft-ietf-manet-packetbb-07.txt, June 2007.

   [2]  Chakeres, I., "Internet Assigned Numbers Authority (IANA)
        Allocations for the Mobile Ad hoc Networks (MANET) Working
        Group", Work In Progress draft-ietf-manet-iana-05.txt,
        June 2007.

   [3]  Clausen, T. and C. Dearlove, "Representing multi-value time in
        MANETs", Work In Progress draft-ietf-manet-timetlv-01.txt,
        June 2007.

   [4]  Clausen, T., Dearlove, C., and B. Adamson, "Jitter
        considerations in MANETs", Work In
        Progress draft-ietf-manet-jitter-01.txt, June 2007.

   [5]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119, BCP 14, March 1997.

   [6]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", October 1998.

17.2.  Informative References

   [7]  Clausen, T. and P. Jacquet, "The Optimized Link State Routing
        Protocol", RFC 3626, October 2003.

   [8]  Macker, J. and S. Corson, "Mobile Ad hoc Networking (MANET):
        Routing Protocol Performance Issues and Evaluation
        Considerations", RFC 2501, January 1999.
















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Appendix A.  Address Block TLV Combinations

   The algorithm for generating HELLO messages in Section 11 specifies
   which addresses may be included in the address blocks after the Local
   Interface Block, and with which associated TLVs.  These TLVs may have
   Type == LINK_STATUS or Type == OTHER_NEIGHB, or both.  TLVs with Type
   == LINK_STATUS may have three possible values (Value == HEARD, Value
   == SYMMETRIC or Value == LOST), and TLVs of TYPE == OTHER_NEIGHB may
   have two possible values (Value == SYMMETRIC or Value == LOST).  When
   both TLVs are associated with the same address only certain
   combinations of these TLV values are necessary, and are the only
   combinations generated by the algorithm in Section 11.  These
   combinations are indicated in Table 5.

   Cells labeled with "Yes" indicate the possible combinations which are
   generated by the algorithm in Section 11.  Cells labeled with "No"
   indicate combinations not generated by the algorithm in Section 11,
   but which are correctly parsed and interpreted by the algorithm in
   Section 12.

   +----------------+----------------+----------------+----------------+
   |                |     Type ==    |     Type ==    |     Type ==    |
   |                |  OTHER_NEIGHB  |  OTHER_NEIGHB, |  OTHER_NEIGHB, |
   |                |    (absent)    |    Value ==    |  Value == LOST |
   |                |                |    SYMMETRIC   |                |
   +----------------+----------------+----------------+----------------+
   | Type ==        |       No       |       Yes      |       Yes      |
   | LINK_STATUS    |                |                |                |
   | (absent)       |                |                |                |
   |                |                |                |                |
   | Type ==        |       Yes      |       Yes      |       Yes      |
   | LINK_STATUS,   |                |                |                |
   | Value == HEARD |                |                |                |
   |                |                |                |                |
   | Type ==        |       Yes      |       No       |       No       |
   | LINK_STATUS,   |                |                |                |
   | Value ==       |                |                |                |
   | SYMMETRIC      |                |                |                |
   |                |                |                |                |
   | Type ==        |       Yes      |       Yes      |       No       |
   | LINK_STATUS,   |                |                |                |
   | Value == LOST  |                |                |                |
   +----------------+----------------+----------------+----------------+

                                  Table 5






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Appendix B.  HELLO Message Example

   An example HELLO message, transmitted by an originator node with a
   single MANET interface, is as follows.  The message uses IPv4 (four
   octet) addresses without prefix TLVs.  The message is transmitted
   with a full message header (message semantics octet is 0) with a hop
   limit of 1 and a hop count of 0.  The overall message length is 50
   octets.

   The message contains a message TLV block with content length 8 octets
   containing two message TLVs, of types VALIDITY_TIME and
   INTERVAL_TIME.  Each uses a TLV with semantics value 8, indicating
   that no start and stop indexes are included, and each has a value
   length of 1 octet.  The values included (0x68 and 0x50) are time
   codes representing the default values of parameters H_HOLD_TIME and
   HELLO_INTERVAL, respectively (6 seconds and 2 seconds) assuming the
   default value of constant C (0.0625 second).

   The first address block contains 1 local interface address.  The
   semantics octet value 2 indicates no address tail, and the head
   length of 4 octets indicates no address mid sections.  This address
   block has no TLVs (TLV block content length 0 octets).

   The second, and last, address block contains 4 neighbor interface
   addresses.  The semantics octet value 2 indicates no address tail,
   the head length of 3 octets indicates address mid sections of one
   octet each.  The following TLV block (content length 7 octets)
   includes one LINK_STATUS TLV which reports the link status values of
   all reported neighbors in a single multivalue TLV: the first two
   addresses are HEARD, the third address is SYMMETRIC and the fourth
   address is LOST.  The TLV semantics value of 40 indicates, in
   addition to that this is a multivalue TLV, that no start and stop
   indexes are included, since values for all addresses are included.
   The TLV value length of 4 octets indicates one octet per value per
   address.
















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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     HELLO     |0 0 0 0 0 0 0 0|0 0 0 0 0 0 0 0 0 0 1 1 0 0 1 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Originator Address                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 1|0 0 0 0 0 0 0 0|    Message Sequence Number    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0| VALIDITY_TIME |0 0 0 0 1 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 1|0 1 1 0 1 0 0 0| INTERVAL_TIME |0 0 0 0 1 0 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 0 1|0 1 0 1 0 0 0 0|0 0 0 0 0 0 0 1|0 0 0 0 0 0 1 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 1 0 0|                     Head                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Head (cont)  |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0|0 0 0 0 0 1 0 0|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0 0 0 1 0|0 0 0 0 0 0 1 1|             Head              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Head (cont)  |      Mid      |      Mid      |      Mid      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Mid      |0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1|  LINK_STATUS  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 1 0 1 0 0 0|0 0 0 0 0 1 0 0|     HEARD     |     HEARD     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   SYMMETRIC   |     LOST      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






















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Appendix C.  Constraints

   Any process which updates the Local Information Base or the
   Neighborhood Information Base MUST ensure that all constraints
   specified in this appendix are maintained.

   In each Local Interface Tuple:

   o  I_local_iface_addr_list MUST NOT be empty.

   o  I_local_iface_addr_list MUST NOT contain any address which is in
      the I_local_iface_addr_list of any other Local Interface Tuple.

   In each Link Tuple:

   o  L_neighbor_iface_addr_list MUST NOT be empty.

   o  L_neighbor_iface_addr_list MUST NOT contain any address which is
      in the I_local_iface_addr_list of any Local Interface Tuple.

   o  L_neighbor_iface_addr_list MUST NOT contain any address which is
      in the L_neighbor_iface_addr_list of any other Link Tuple in the
      same Link Set.

   o  If L_HEARD_time has not expired then there MUST be a Neighbor
      Tuple whose N_neighbor_iface_addr_list contains
      L_neighbor_iface_addr_list.

   o  L_HEARD_time MUST NOT be greater than L_time.

   o  L_SYM_time MUST NOT be greater than L_HEARD_time (unless both are
      expired).

   o  L_quality MUST NOT be less than 0 or greater than 1.

   o  If L_quality >= HYST_ACCEPT then L_pending MUST be false.

   o  If L_quality < HYST_REJECT then L_status MUST be PENDING or LOST.

   o  L_pending MUST NOT be set to true if it is currently false.

   In each Neighbor Tuple:

   o  N_neighbor_iface_addr_list MUST NOT contain any address which is
      in the I_local_iface_addr_list of any Local Interface Tuple.

   o  N_neighbor_iface_addr_list MUST NOT contain any address which is
      in the N_neighbor_iface_addr_list of any other Neighbor Tuple.



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   o  If N_symmetric == true, then there MUST be one or more Link Tuples
      with:

      *  L_neighbor_iface_addr_list contained in
         N_neighbor_iface_addr_list; AND

      *  L_status == SYMMETRIC.

   o  If N_symmetric == false, then there MUST be one or more Link
      Tuples with:

      *  L_neighbor_iface_addr_list contained in
         N_neighbor_iface_addr_list.

      All such Link Tuples MUST NOT have L_status == SYMMETRIC.  At
      least one such Link Tuple MUST have L_HEARD_time not expired.

   In each Lost Neighbor Tuple:

   o  NL_neighbor_iface_addr MUST NOT be in the I_local_iface_addr_list
      of any Local Interface Tuple.

   o  NL_neighbor_iface_addr MUST NOT equal the NL_neighbor_iface_addr
      of any other Lost Neighbor Tuple.

   o  NL_neighbor_iface_addr MUST NOT be in the
      N_neighbor_iface_addr_list of any Neighbor Tuple with N_symmetric
      == true.

   In each 2-Hop Tuple:

   o  There MUST be a Link Tuple associated with the same MANET
      interface with:

      *  L_neighbor_iface_addr_list == N2_neighbor_iface_addr_list; AND

      *  L_status == SYMMETRIC.

   o  N2_2hop_iface_addr MUST NOT be in the I_local_iface_addr_list of
      any Local Interface Tuple.

   o  N2_2hop_iface_addr MUST NOT be the N2_2hop_iface_addr of any other
      2-Hop Tuple in the same 2-Hop Set and with the same
      N2_neighbor_iface_addr_list.

   o  N2_2hop_iface_addr MUST NOT be in the N2_neighbor_iface_addr_list
      of the same 2-Hop Tuple.




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Appendix D.  Security Considerations

   The objective of this protocol is to allow each node in the network
   to acquire information describing its 1-hop and symmetric 2-hop
   neighborhoods.  This is acquired through message exchange between
   neighboring nodes.  The information is made available through a
   collection of sets, describing the node's 1-hop neighborhood and
   symmetric 2-hop neighborhood.

   Under normal circumstances, the information recorded in these sets is
   correct - i.e. corresponds to the actual network topology, apart from
   any changes which have not (yet) been tracked by the HELLO message
   exchanges.

   If some node for some reason, malice or malfunction, injects invalid
   HELLO messages, incorrect information may be recorded in the sets
   maintained.  The protocol specification does, however, prevent
   inconsistent information from being injected in the protocol sets
   through the constraints in Appendix C.  The exact consequence of
   information inexactness depends on the use of these sets, and should
   be reflected in the specification of protocols which use information
   provided by NHDP.

   This appendix, therefore, only outlines the ways in which correctly
   formed, but still invalid, HELLO messages may appear.

Appendix D.1.  Invalid HELLO messages

   A correctly formed, but still invalid, HELLO message may take any of
   the following forms:

   A node may provide false information about its own identity:

      *  The Local Interface Block of the HELLO message may contain
         addresses which do not correspond to addresses of interfaces of
         the node transmitting the HELLO message.

      *  The Local Interface Block of the HELLO message may omit
         addresses of interfaces of the local node transmitting the
         HELLO message.

      *  The Local Interface Block may contain additional OTHER_IF TLVs,
         indicating incorrectly that an address is associated with an
         interface other than that over which the HELLO message is
         transmitted.

      *  The Local Interface Block may omit OTHER_IF TLVs, thereby
         indicating incorrect addresses associated with the MANET



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         interface over which the HELLO message is transmitted.

   A node may provide false information about the identity of other
   nodes:

      *  A present or absent address in a Neighbor Block, does not in
         and by itself cause a problem.  It is the presence, absence, or
         incorrectness of associated LINK_STATUS and OTHER_NEIGHB TLVs
         that causes problems.

      *  A present LINK_STATUS TLV may, incorrectly, identify an address
         as being of a MANET interface which is or was heard on the
         MANET interface over which the HELLO message is transmitted.

      *  A consistently absent LINK_STATUS TLV may, incorrectly, fail to
         identify an address as being of a MANET interface which is or
         was heard on the MANET interface over which the HELLO message
         is transmitted.

      *  A present OTHER_NEIGHB TLV may, incorrectly, identify an
         address as being of a node which is or was in the sending
         node's symmetric 1-hop neighborhood;

      *  A consistently absent OTHER_NEIGHB TLV may, incorrectly, fail
         to identify an address as being of a node which is or was in
         the sending node's symmetric 1-hop neighborhood;

      *  The value of a LINK_STATUS TLV may incorrectly indicate the
         status (LOST, SYMMETRIC or HEARD) of the link from a 1-hop
         neighbor.

      *  The value of an OTHER_NEIGHB TLV may incorrectly indicate the
         status (LOST or SYMMETRIC) of a symmetric 1-hop neighbor.


















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Appendix E.  Flow and Congestion Control

   This protocol specifies one message type, the HELLO message.  The
   maximum size of a HELLO message is proportional to the size of the
   originating node's 1-hop neighborhood.  HELLO messages MUST NOT be
   forwarded.

   A node MUST report its 1-hop neighborhood in HELLO messages on each
   of its MANET interfaces at least each REFRESH_INTERVAL.  This puts a
   lower bound on the control traffic generated by each node in the
   network employing this protocol.

   A node MUST ensure that two successive HELLO messages sent on the
   same MANET interface are separated by at least HELLO_MIN_INTERVAL.
   (If using jitter then this may be reduced to a mean minimum value of
   HELLO_MIN_INTERVAL - HP_MAXJITTER/2.)  Thus, this puts an upper bound
   on the control traffic generated by each node in the network
   employing this protocol.

































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Appendix F.  Contributors

   This specification is the result of the joint efforts of the
   following contributors -- listed alphabetically.

   o  Brian Adamson, NRL, USA, <adamson@itd.nrl.navy.mil>

   o  Cedric Adjih, INRIA, France, <Cedric.Adjih@inria.fr>

   o  Emmanuel Baccelli, Hitachi Labs Europe, France,
      <Emmanuel.Baccelli@inria.fr>

   o  Thomas Heide Clausen, PCRI, France, <T.Clausen@computer.org>

   o  Justin Dean, NRL, USA, <jdean@itd.nrl.navy.mil>

   o  Christopher Dearlove, BAE Systems, UK,
      <Chris.Dearlove@baesystems.com>

   o  Philippe Jacquet, INRIA, France, <Philippe.Jacquet@inria.fr>































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Appendix G.  Acknowledgements

   The authors would like to acknowledge the team behind OLSRv1,
   specified in RFC3626 for their contributions.

   The authors would like to gratefully acknowledge the following people
   for intense technical discussions, early reviews and comments on the
   specification and its components: Joe Macker (NRL), Alan Cullen (BAE
   Systems), and the entire IETF MANET working group.










































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Authors' Addresses

   Thomas Heide Clausen
   LIX, Ecole Polytechnique, France

   Phone: +33 6 6058 9349
   Email: T.Clausen@computer.org
   URI:   http://www.ThomasClausen.org/


   Christopher Dearlove
   BAE Systems Advanced Technology Centre

   Phone: +44 1245 242194
   Email: chris.dearlove@baesystems.com
   URI:   http://www.baesystems.com/


   Justin W. Dean
   Naval Research Laboratory

   Phone: +1 202 767 3397
   Email: jdean@itd.nrl.navy.mil
   URI:   http://pf.itd.nrl.navy.mil/


   The OLSRv2 Design Team
   MANET Working Group























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Full Copyright Statement

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